Robot system

ABSTRACT

This invention relates generally to robots and specifically to a robot for spraying applications which has the ability to accurately follow trajectories that require high speeds and accelerations, a working envelope appropriate for processing the sides, top, and bottom of a large object such as an aircraft, an integrated revolute joint and actuator for supplying power to the movable components of the robot along protected, low maintenance power paths, a zero backlash drive, and a gravity compensating system which causes the robot to be neutrally balanced throughout its entire working envelope even while carrying a payload of significant weight.

BACKGROUND OF THE INVENTION

Robot systems for coating, and specifically paint spraying, are now wellestablished particularly for production line use in applications inwhich relatively flat, easy to access surfaces are presented to thespray gun such as parts moving along an assembly line The robot movesand coordinated gun operations in such systems are relatively simple andhave been developed to a high degree

A need exists, however, for a robot spray gun system which is adapted toapply coatings to large, non-regular surfaces in a very precise andcontrolled pattern. One such application is the aerospace industry wherelarge, irregularly shaped structures must be coated. An airplane is agood example of such an application. Today's aircraft standards areexceedingly high as compared to only a few years ago and present robotsystems are either too slow, not sufficiently accurate, cannot accessall surfaces, or not cost efficient, and usually a combination of someor all of the foregoing Military aircraft, for example, may require upto 50 very thin coating applications on some exposed surfaces, and thetime required to meet this standard with present equipment isunacceptably long and, often, of insufficient quality. As will beappreciated such structures as airplanes have flat surfaces, numerousjunctions, but mostly curvilinear contours, all of which dictate thatthe robot must operate with a very high degree of precision.

Accordingly, objectives of this invention are to provide a robot withthe ability to follow complex trajectories that require widely varyingspeeds and high acceleration, an enormous useful work envelope, lowmaintenance, particularly as regards malfunction of hydraulic andelectrical lines and components which, because of their generallyexposed conditions, are subject to damage and consequent malfunction,and counter balanced coating application; i.e., a coating applicatorwhich has the capacity of near instantaneous response to motion commandsdue in part to the absence of gravitational torque in the system.

In a specific embodiment of the invention a fully integrated robotsystem is provided which is capable of painting an entire aircraft Thesystem includes a transporter sub-system which carries a robotsub-system. The transporter is provided with three degrees of freedom,namely, a vertical; i.e., a Z axis movement for the entire system, afirst horizontal rotational movement provided by a first-boom whichrotates about the Z axis, and a second horizontal rotational movementprovided by a second boom or arm which rotates about a vertical axiscarried by the first boom at the point of attachment of the first boomto the second boom. The robot sub-system has six degrees of freedom,said sub-system being mounted at the end of the second boom or arm ofthe transporter. Preferably the robot sub-system has a first degree offreedom about a vertical axis, a second degree of freedom about a firsthorizontal axis, a third degree of freedom about a second horizontalaxis which is parallel to the first horizontal axis, and a wristmechanism capable of movements about roll, pitch, and yaw axis.

Further attributes of such a system are that (i) the work envelope isdramatically increased over prior systems, (ii) oil connections are madethrough integrated multi-port swivel fittings, (iii) all leak pathsdrain back to tank thus making the system virtually leak free, (iv) thehydraulic connections are totally enclosed within the robot arm and baseand therefore protected to the maximum extent possible which results inlow maintenance and a smooth, clean look, (v) overhanging structureswhich currently are common are not present, (vi) reliability isincreased, and (vii) the work envelope has redundant access to achieve100% attainability to all surfaces to be coated.

BRIEF DESCRIPTION OF THE DRAWING

The invention is illustrated more or less diagrammatically in theaccompanying drawing in which

FIG. 1 is a perspective of the robot system of this invention as appliedto the coating of a military airplane;

FIG. 2, which consists of sub-parts 2A and 2B, illustrates thetransporter sub-system with the work envelope shown in phantom in FIG.2B;

FIG. 3 is a view taken substantial along the line 3--3 of FIG. 2Ashowing the backlash-free drive system which provides near instantaneousresponse to system commands;

FIG. 3A is a diagrammatic illustration of the hydraulic system for thedrive system shown best in FIGS. 2A and 3;

FIG. 4 is a view partly in section, of the joint between the two boomsor arms of the transporter sub-system;

FIG. 5 is a view taken substantially along the line 5--5 of FIG. 4;

FIG. 6 is an axial section of an integrated revolute joint and actuatorfor the robot arm sub-system of FIG. 2B;

FIG. 7A is an elevation showing the upper arm in positions of maximumgravitational torque;

FIG. 7B is an elevation showing the upper arm of the robot sub-system ina position of minimum gravitational torque;

FIG. 8A is an elevation showing the lower arm of the robot armsub-system in positions of minimum gravitational torque;

FIG. 8B is an elevation showing the lower arm of the robot armsub-system in positions of maximum gravitational torque;

FIG. 9 is a plan view of the gravitational torque compensating cylindersand the power train for the upper arm of the robot arm sub-system;

FIG. 10 is an elevation of the portion of the robot arm sub-system shownin FIG. 9; and

FIG. 11 is a plan view in section of the power transfer through the baseof the robot arm sub-system of FIG. 9.

Referring first to FIGS. 1-5, and initially to FIG. 1, a work piece tobe coated, in this instance a military airplane, is indicated generallyat 10. As will be noted the plane has several relatively flat surfaces,such as the wing sections 11 and 12 and tail section 13, but it iscomposed mainly of curved surfaces 14, 15 which meet at numerousjunctions 16. Some of the curved surfaces are uniformly curved andothers are not.

The plane is supported by work stands 17 and 18 to keep it in a fixedposition for coating. For purposes of description the coating willhereafter be referred to as paint.

Three robot systems of this invention are indicated generally at 20, 21,and 22. In this instance three robot systems have been found sufficientto paint the plane and all are operated simultaneously by a controller,not shown. Since the construction and operation of each system isidentical, only one will be described in detail.

Robot system 20 is composed of a transporter sub-system, indicatedgenerally at 23, and a robot sub-system, indicated generally at 24. Thetransporter sub-system includes hydraulic column 26 which reciprocatesalong a vertical or Z axis. The column 26 projects from a housing 27whose upper edge is flush with the plane of the floor 28. A first boomor arm 29 is carried by and rotatable with the upper end of column 26. Ahalf-bubble housing 30 covers and protects the upper end of thehydraulic column and the joint between the column and boom 29. A secondboom is indicated at 31, said second boom being mounted on the distalend of boom 29 and rotatable about a vertical axis 32, see FIGS. 2A and4, at the end of boom 29.

The robot arm sub-system 24 includes a base 34, a lower arm 35, and anupper arm 36. A paint spray gun 37 is attached to a wrist mechanism thatis carried at the outer end of the upper arm 36. It will be understoodthat pitch and yaw and roll movements are attainable by the paint spraygun, but since this invention is not specifically directed to themounting and movement of the spray guns, this feature is not furtherdescribed. The vertical axis about which the base 34 rotates isindicated at 38, see FIG. 2B, the horizontal axis about which the lowerarm 35 rotates is indicated at 39, see FIG. 2B, and the horizontal axisabout which upper arm 36 rotates is indicated at 40, see FIG. 2B.

From FIGS. 2B, 7B, 9 and 10 it will be noted that the work envelope andthe robot arm sub-system is very large, a vertical cross section ofwhich is indicated at 42 in FIG. 2B.

The transporter sub-system 23 is best illustrated in FIGS. 2, 3, 4 and5.

In FIG. 2A the hydraulic column 26 is shown in a near-fully retractedposition in its stationery sleeve or housing 44. Sleeve 44 is held in anexact vertical position by a frame work 45 which includes a plurality ofvertical, angled reinforcing struts 46.

A mounting plate 53 is carried by the upper end of column 26. A ringgear mount 54 is releasably secured to mounting plate 53 by bolts 55,and a ring gear 56 is mounted on the gear mount 54 by any suitablemeans.

The transporter arm mounting shaft is indicated at 58. The shaft issecured to ring gear mount 54 by bolts 59. The first boom 29 rotatesabout the transporter arm shaft 58 on bearings not numbered Thus boom 29rotates about shaft 58 which is fixed with ring gear 56, and thehydraulic column 26.

Means for rotating boom 29 are illustrated best in FIGS. 2A, 3 and 3A.

Hydraulic motor means are indicated generally at 61 in FIG. 2A and aspeed reducer at 62. An output shaft is indicated at 63 in FIGS. 2A and3. From FIGS. 3 and 3A it will be seen that a second hydraulic motormeans 67 and speed reducer arrangement drives a second shaft 64. Shafts63, 64 drive spur gears 65, 66, respectively, which engage ring gear 56.From FIGS. 3 and 3A it will be noted that during operation the motor 61,67 continuously operate in opposition to one another with respect to thering gear 56. Thus, when motor 61 drives ring gear 26 in a clockwisedirection, motor 67 will exert an opposing, driving force on ring gear26 in a counter-clockwise direction. However, since the clockwisedriving force of motor 61 may be 100-ft-lbs, and the counter-clockwisedriving force of motor 67 may be only 10 ft-lbs, the net result will bea clockwise driving force to 90-ft-lbs. through valving 68 and itsassociated circuitry 69. It will further be noted that, depending on theposition of control valve spool 57, one of motors 61 or 67 willoverpower the other and drive against it. As a consequence ring gear 56will, almost instantaneously upon decrease in driving power from themotor which is dominant at a given moment, rotate in the oppositedirection under control of the other motor which takes over as thedominant driver This instant response is essential to achieving a quickchange of direction at the spray head when the contour of the work piecechanges, all as earlier described. This drive system eliminates backlashas both pinions experience torque in only one direction and one and onlyone side of a tooth is ever in contact with the ring gear.

The mounting of second or outer boom 31 to the first or inner boom 29 isillustrated best in FIGS. 2A, 4 and 5. From FIGS. 2A and 4 it will beseen that a motor and pivot support housing 70 is secured to the outerend of boom 29. The housing carries bearings 71, 72 which support asecond boom shaft 73 to which the second boom 31 is secured as bywelding. The shaft and boom is powered by motor 74 which drives a powershaft 75 through a gear reducer 76. Power shaft 75 is keyed to boomshaft 73 by keys 77. Hence, as second boom 31 rotates about axis 32, therobot arm assembly of FIG. 2B will swing in horizontal arcs about axis32.

An integrated revolute joint and actuator is illustrated best in FIGS.2B and 6. This feature makes possible the placement of all air, oil anddrain within the links in the robot arm sub-system so that thepossibility of malfunction due to accidental contact with exposed linesis eliminated. This feature also provides a continuous pressurelubricated joint which is very compact and efficient.

Referring first to FIG. 2B it will be seen that outer boom arm 31includes a robot arm sub-system mounting platform, indicated generallyat 80, which is secured to the outer end of arm 31 by struts 81 andbraces 82. The integrated revolute joint and actuator is indicatedgenerally 83 and is bolted to the platform base 84 of the mountingplatform 80, as indicated in FIG. 6.

The joint-actuator includes a valve body 85 having a mounting flange 86by which it may be bolted to platform base 84. A valve body end cap isindicated at 87, and a close off end cap at 88. The base plate 89 of therobot arm sub-assembly, which will be described hereinafter, is boltedto valve spool 90 by bolts 91 and hence the base plate 89, and thus therobot arm sub-system rotates with respect to boom arm 31 about verticalaxis 38. Upper and lower spaced bearings are indicated at 92, 93respectively, and a bearing retaining ring is shown at 94.

A hydraulic motor is indicated at 96, its output shaft at 97, and a gearreducer at 98 It will be understood that the output shaft 97 of motor 96engages a drive gear within the gear reducer, which drive gear in turnengages planetary gears which in turn engage an internal ring gear, allin a conventional manner. Since the housing of the gear reducer 98 whichcarries the inner planetary gear is secured to the valve body by bolts99, it will be seen that rotation of motor 96 will cause base plate 89,and hence the robot arm sub-system, to rotate with respect to boom arm31.

A plurality of circumferential passages are formed in the periphery ofvalve spool 90 at 100, 101, 102, 103, 104, and 105. These may be, forexample, for air to joint 3 (100), air to joint 2 (101), air to joint 1(102), hydraulic drain (103), hydraulic pressure (104), and hydraulicreturn (105). In the exemplary showing of FIG. 6, an internal verticalpassageway 106 in the valve spool 108 connects hydraulic pressurepassageway 104 with a pressure hose 107 to motor 96 for driving themotor in a desired direction The circular pressure passageway 104 would,in turn, connect with an outlet port in the valve body 108 which wouldin turn connect to a hydraulic pressure line from a pump or other sourceof pressure so that high pressure liquid can drive the motor. By way offurther illustration, the drain passageway 103 is, in the positionshown, in communication with a radial passage 109 which connects with adrain hose, not shown.

Further, a return port 110 in the valve body communicates with circularreturn passageway 105 in the valve spool to provide a path for liquidfrom downstream joint/actuators to return to tank through joint/actuator83. It will be understood that the return line from motor 96 willconnect with a vertical passage similar to pressure passage 106, but ata different peripheral location, which in turn will open into passage105 so that spent fluid from motor 96 can return to tank.

By arranging the air and oil lines in this fashion all piping can beinternalized within the robot arm sub-system, to be described hereafter,so that all joints are lubricated under pressure and the risk ofexternal leaks, injury, or damage to the fluid is virtually eliminated.

The robot sub-system 24, and particularly the gravitational compensatingfeature thereof, is illustrated best in FIG. 7A, 7B, 8A, 8B, 9, 10, and11 to which reference is now made. It will be understood as discussedabove that precise control of the paint spray gun 37 is essential incritical applications, such as coating aerospace vehicles, and thatattainment of precise control in a system of the type herein describedis very difficult in view of the long cantilever effect of the robotsub-system about the transporter axis 33, see FIG. 2A, of the hydrauliccolumn 26 The gravitational compensating system in the above Figuresenables precise control to be obtained so that the tight performancespecifications which this system must meet are attained.

Referring first to FIGS. 9, 10, and 11 the robot base of the robotsub-system is indicated at generally 115, base 115 including base plate89 As best seen in FIG. 9, lower arm 35 of the robot arm sub-system islinked to robot base 115 about horizontal axis 39, and the upper arm 36of the robot arm sub-system is linked to the lower arm about upper armaxis 40. Upper arm 35 is offset from lower arm 36.

The system for rotating lower arm 35 about horizontal axis 39 includespneumatic arc cylinder 116 whose inner, or left, end in this instance ismounted for pivotal rotation about a pivot bar 117 which is seated inblocks 118, 119 which are fast with robot base 115. Piston rod 120 ofcylinder 116 is pivotally connected as at 121 to crank links 122, 123.The outer end of link 122 is fast with stub shaft 124 which is receivedin a shaft seat 125 which in turn is fast with the base 115. Crank link123 is fast with a shaft 126 which is co-axial with stub shaft 124.Shaft 126 is received in bearing 127 which is seated in a recess incenter wall 128 of the robot base 115. Shaft 126 is fast with a gearcase 129 which contains a planetary gear system. The outer rim of theplanetary gear system is bolted to a valve spool 130 by a plurality ofbolts, two of which are indicated at 131, 132. The spool 130 is, inturn, bolted to lower arm 35 by a plurality of bolts, one of which isindicated at 133.

It will thus be seen that when piston rod 120 is extended and retracted,arm 35 will rotate about the horizontal axis 39 of shafts 124, 126through valve spool 130. The degree of movement is such that arm 35 canbe positioned at all locations required to define envelope 42 and,preferably, 360 degrees. When arm 35 is rotated to the solid lineposition of FIGS. 1 and 8A, and the phantom of FIG. 8A, thegravitational torque attributable to arm 35 will be a minimum. Momentarm calculations within the skill of the art about axis 39 as areference point will disclose that with constant pressure of a valvedependent on the weight of the lower arm 35 supplied to cylinder 116 thesum of the opposing moments equals zero whereby the effect of the weightof arm 35 is effectively reduced to zero and hence all the poweravailable from the joint actuator can be used to accelerate the motionof the arm.

The system for rotating upper arm 36 about axis 40 includes a smallcylinder 135 whose inner or left end in this instance is mounted forpivotal rotation about pivot bar 117. Piston rod 136 of cylinder 135 ispivotally connected as at 137, see FIG. 10, to upper arm crank links138, 139. The outer end of link 138 is fast with stub shaft 140 which isrotatably received in a shaft seat 141 carried by center wall 128 ofrobot base 115. The outer end of link 139 is fast with a shaft 142 whichis co-axial with shaft 140. Shaft 142 is received in a bearing, notshown in FIGS. 9 or 11, which is seated in a recess in wall 143.

Shaft 142 is fast with a first drive sprocket 144 which drives sprocket145 through roller chain 146, see FIG. 10, over a tension adjustmentidler 147. Sprocket 145 is secured to a power transmission sleeve 148,see FIG. 11, which in turn is carried by the valve body 149, the valvebody 149 receiving the valve spool 130.

A second or slave drive sprocket is indicated at 150, said secondsprocket 150 being fast with the power sleeve 148. It will thus be seenthat sprocket 145 functions as a driven sprocket; i.e.: with respect tofirst drive sprocket 144, and, also, as a driving sprocket; i.e.: withrespect to second or slave sprocket 150. Second drive sprocket 150drives an upper arm sprocket 151 through roller chain 152 and overtensioning idler 153. Upper ar sprocket 151 is fast with a drive sleeve154 which, in turn, is secured by any suitable means to the robotsub-system upper arm 36.

It will thus be seen that when piston rod 136 is extended and retracted,the robot sub-system upper arm 36 will rotate about the axis 40 of upperarm shaft 155. The degree of movement is such that arm 36 can bepositioned, in conjunction with arm 35, in all locations required todefine envelope 42 and, preferably 360 degrees. When arm 36 is rotatedto the position of FIGS. 7B and 8B, the gravitational torqueattributable to arm 36 will be a minimum. Moment calculations within theskill of the art about axis 40 will disclose that with constantpressure, of a valve that depends on the weight of the arm 36 and thepayload supplied to cylinder 135 the sum of the opposing moments equalszero whereby the effects of the weight of the payload and the weight ofthe arm 36 is effectively reduced to zero, and hence all the poweravailable from the joint/actuator can be used to accelerate the upperarm and payload. By comparison, when arm 36 is in the position of FIGS.1, 2B, 7A, 9 and 10, the gravitational torque attributable to arm 36will be at a maximum and hence the piston arm 136 is operated to movecrank arms 138, 139 to their positions of FIGS. 7A so that the sum ofthe moments continue to balance out.

The end result is a symmetrical response to commands from the systemcontroller since the arms 35 and 36 are always operated by cylinders 116and 135 to maintain zero gravitational torque and reduced risk of injuryor damages as the arms will not fall if power is lost.

It will be understood that an integrated revolute joint and actuatorsimilar to that described in conjunction with FIG. 6 is located at thejunction of robot base 115 and arm 35, and also at the junction of arms35 and 36 so that hydraulic and pneumatic power can be transmittedthrough the robot arm sub-system to all actuators in the system with theresult that intricate movements can be achieved as required by the workpiece 10.

Although a preferred embodiment of the invention has been illustratedand described, it will be apparent to those skilled in the art thatmodifications may be made within the spirit and scope of the invention.Accordingly it is intended that the scope of the invention be definednot by the foregoing exemplary description but solely by the scope ofthe hereafter appended claims when interpreted in view of the relevantprior art.

We claim:
 1. In a robot system having a first arm which is swingableabout a first axis of rotation and arm extension means carried by andextending outwardly beyond the outer end portion of the first arm, thecombination ofa main gear operatively connected to the inner portion ofthe first arm, and drive means for said main gear, said drive meansincluding means for rotating said first arm about said first axis in onedirection of rotation, means for rotating said first arm about saidfirst axis in the opposite direction of rotation, and means foreliminating backlash in said main gear and its driving system upon achange in the direction of rotation, said means for eliminating backlashbetween said main gear and its driving system including a first drivegear in engagement with said main gear, first hydraulic motor meanswhich applies a constant preload torque to said first drive gear in adirection to drive said main gear in a first direction, a second drivegear in engagement with said main gear, second hydraulic motor meanswhich applies a constant preload torque to said second drive gear in adirection to drive said main gear in a second direction opposed to saidfirst direction, and means for selectively applying a driving torquegreater than said preload torque to one of said drive gears to therebyoverpower said other drive gear by said one drive gear and thereby drivethe main gear in the direction of the drive gear to which said greatertorque has been applied, and vice versa, whereby no dwell time occursbetween rotation direction changes of said main gear resulting from theoverpowering of a drive gear by the remaining drive gear and backlash iseliminated.
 2. The combination of claim 1 further characterized inthatsaid selective torque applying means includes a common hydrauliccircuit connecting the two motors and valve means in the hydrauliccircuit for applying a greater hydraulic pressure to a selected one ofthe two drive gears.
 3. The robot system of claim 1 furthercharacterized in that said first axis of rotation is vertical.
 4. Thecombination of claim 3 further characterized in thatsaid means foreliminating backlash between said main gear and its driving systemincludes a first drive gear in engagement with said main gear, firsthydraulic motor means which applies a constant preload torque to saidfirst drive gear in a direction to drive said main gear in a firstdirection, a second drive gear in engagement with said main gear, secondhydraulic motor means which applies a constant preload torque to saidsecond drive gear in a direction to drive said main gear in a seconddirection opposed to said first direction, and means for selectivelyapplying a driving torque greater than said preload torque to one ofsaid drive gears to thereby overpower said other drive gear by said onedrive gear and thereby drive the main gear in the direction of the drivegear to which said greater torque has been applied, and vice versa,whereby no dwell time occurs between rotation direction changes of saidmain gear resulting from the overpowering of a drive gear by theremaining drive gear and backlash is eliminated.
 5. The combination ofclaim 4 further characterized in thatsaid selective torque applyingmeans includes a common hydraulic circuit connecting the two motors andvalve means in the hydraulic circuit for applying a greater hydraulicpressure to a selected one of the two drive gear.